The present invention relates to a thermal energy storage system. More particularly, the present invention relates to a thermal energy storage system including at least one thermal storage apparatus configured to be incorporated into the heating and cooling system of a vehicle or the like.
Use of heating and cooling systems for vehicular applications is common and well established to maintain a comfortable environment within the vehicle while the vehicle engine is operating. When the occupants of the vehicle stop driving and rest in the vehicle, the interior space in the vehicle can become very uncomfortable due to the air temperature within the vehicle increasing or decreasing. In most vehicles, the heating and cooling system maintains comfort levels within the vehicle only during engine operation. These heating and cooling systems do not provide space conditioning to the interior of the vehicle when the engine is turned off.
Phase change materials ("PCMs") store heat during phase transition, typically liquid/solid phase transitions. For example, water, paraffins, alcohol, salts and salt hydrates have notably high energy densities over temperature ranges of practical significance. A large amount of thermal energy can be stored as latent heat of fusion during the melting of an appropriate PCM. The stored heat can then be extracted from the liquid PCM by cooling it until it crystallizes. Thermal energy can also be stored as sensible heat in PCMs.
Various attempts have been made to incorporate PCMs into heating and air conditioning systems, including heat pump systems, solar collection systems, and more conventional heating and air conditioning systems. For example, U.S. Pat. No. 5,054,540 to Carr describes a cool storage reservoir positioned in the air duct of a vehicle or the like. A plurality of elongated sealed containers are positioned in the cool storage reservoir, each of the sealed containers being filled with a gas/water medium capable of forming a gas hydrate. U.S. Pat. No. 5,277,038 to Carr also implements a thermal storage system into a vehicle using gas hydrates.
Gas hydrates, however, may possess a variety of disadvantages. Gas hydrates suffer from the development of significant pressures during decomposition and may be subject to excessive supercooling. They may also require specific devices to initiate nucleation. Another disadvantage of the U.S. Pat. No. 5,277,038 patent is that the vehicle's air distribution system is required to discharge the stored thermal energy. The vehicle air distribution system has a powerful blower which drains power out of the batteries very fast. Further, the U.S. Pat. No. 5,277,038 patent discloses storing high and low temperature thermal energy of the same temperature. This does not permit the system of the U.S. Pat. No. 5,277,038 patent to provide comfortable thermal conditioning of a vehicle interior. In addition, the system disclosed in the U.S. Pat. No. 5,277,038 patent is not compatible with electric powered vehicles (EV) which don't have vehicle heating and cooling systems.
Another example is the "heat battery" designed to provide "instant" heating to a vehicle cabin. (Automotive Engineering, Vol. 100, No. 2, Feb. 1992). The core of the heat battery includes a series of flat, sheet metal PCM envelopes in spaced-apart relationship. The heat battery and an electric coolant pump are installed in a coolant line running from the engine to the cabin heater, forming a closed circuit capable of very rapidly heating the cabin when the engine is turned on.
While such a design possesses certain advantages in typical passenger vehicle applications, there remains a need for thermal storage system designs which can be operated more flexibly. For example, there remains a particular need for a thermal storage system which can provide space conditioning for several hours to an enclosed space when the engine is off.
According to the present invention, a thermal energy storage system is provided for heating and cooling the interior occupied spaces of a vehicle when the vehicle engine is turned off. While the vehicle engine is operating, either heating effect from a connection to the engine's coolant system or cooling effect from a connection to the refrigerant flow in the vehicle's air conditioning system is obtained and circulated through PCMs for absorption. When the engine is turned off, the previously stored thermal energy is released to warm or cool the interior occupied spaces of the vehicle to maintain a comfortable environment. In addition, this thermal energy may be withdrawn from storage and circulated through the engine's coolant system either prior to, or upon start-up, to warm up the engine and related vehicle components, such as a battery. Initiation of circulation from storage to this coolant loop, either prior to or upon engine start-up, can expedite the engine's ability to obtain optimal operating temperatures, thus greatly improving emission control and heater coil performance. Further, temperature maintenance within the battery greatly improves reliability, charge acceptance, and lifetime.
In the several embodiments of the present invention, the thermal energy storage system includes a thermal storage apparatus that houses the PCMs. The refrigerant flow and coolant flow is plumbed directly to the thermal storage apparatus so that the refrigerant flow and coolant flow circulate through the thermal storage apparatus.
One feature of a thermal storage apparatus in accordance with the present invention is that the refrigerant flow and coolant flow circulate through the thermal storage apparatus in coils. This feature permits the hot coolant and cool refrigerant to be in direct contact with the PCM.
Advantageously, the thermal energy storage system is a modular and self-sufficient component requiring connection only to the vehicle's coolant system and refrigerant lines. Further, it is configured for both new and retrofit installations. The thermal energy storage system should have little effect on the operating performance of the vehicle's conventional heating and cooling system.
Another feature of the present invention is that it can supplement a vehicle coolant system to prevent the vehicle engine from overheating during extreme load conditions. This is advantageous when the vehicle is designed with an undersized radiator.
In alternative embodiments of the present invention, the thermal energy storage system may be used for conditioning of building spaces with similar "off-peak" charging of the system, awaiting "on-peak" discharge. Use of a thermal energy storage system for standby emergency space conditioning can provide significant benefit to building spaces and electronic equipment that are temperature sensitive or that may suffer failure if conventional heating and cooling systems are unavailable.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.